Wind power installation with contactless power transmitter

ABSTRACT

A wind power installation for producing a sinusoidal ac voltage is disclosed. Briefly described, one embodiment comprises a generator having a generator rotor and a generator stator; a rotor unit with rotor blades which are connected to the generator rotor; and a power transmission means for the transmission of electrical power from the non-rotating part of the wind power installation to the rotor unit, the power transmission means having an asynchronous machine whose stator is arranged at the non-rotating part of the wind power installation and whose rotor is arranged at the rotor unit for contactless transmission of electrical power to the rotor unit, and arranged in the non-rotating part of the wind power installation is an inverter for producing an ac voltage having a periodic voltage pulse for feeding the stator of the asynchronous machine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a wind power installation for producing asinusoidal ac voltage comprising a generator having a generator rotorand a generator stator, a rotor unit with rotor blades which isconnected to the generator rotor, and power transmission means for thetransmission of electrical power from the non-rotating part of the windpower installation to the rotor unit.

2. Description of the Related Art

In the case of wind power installations it is necessary for power to betransmitted from the non-rotating part to the rotating part, for variouspurposes. For example, in the case of an electromagnetically excitedsynchronous generator, a direct current is required as the excitercurrent for the pole wheel, and for rotor blade adjustment by means ofsuitable electric motors that also requires electrical power. At thepresent time that power is transmitted from the non-rotating part of thewind power installation to the rotating part by means of slip rings.Slip rings however basically suffer from the disadvantage that lossesoccur by virtue of the friction involved, that is to say the level ofefficiency is reduced, a large amount of noise is generated, and inparticular they suffer from a high level of wear, and therefore need tobe repaired or have to be replaced from time to time. In additionelectrical flash-overs can occur at such slip rings. They are evenfurther promoted with increasing operating time, due to the abrasion ofparticles.

DE 198 01 803 A1 discloses an electrical rotational machine with astationary stator and a rotatable rotor. In that case they have a statortransformer winding and a rotor transformer winding respectively,wherein the transformer windings form an electrical transformer and areeach designed for operation with alternating current. By means of thetransformer windings a three-phase current which is fed in from a supplynetwork can be transmitted to the rotating part of the wind powerinstallation, and is then fed to the three-phase current, generatorwinding disposed in the stator of the generator of the wind powerinstallation, for excitation purposes.

U.S. Pat. No. 5,770,909 describes a synchronous machine for electricallyoperated vehicles, with which the power of the generator is to beoptimised for all travel conditions, in particular over a rotary speedrange of from zero to several thousand revolutions per minute.

BRIEF SUMMARY OF THE INVENTION

Therefore the object of the present invention is to provide an improvedway of transmitting the electrical power from the non-rotating part ofthe wind power installation to the rotating part.

In accordance with the invention, starting from the wind powerinstallation set forth in the opening part of this specification, thatobject is attained in that the power transmission means have anasynchronous machine whose stator is arranged at the non-rotating partof the wind power installation and whose rotor is arranged at therotating part for contactless transmission of electrical power to therotating part and that arranged in the non-rotating part of the windpower installation is an inverter for producing an ac voltage having aperiodic voltage pulse for feeding the stator of the asynchronousmachine.

In that respect the invention is based on the realisation thatmechanical problems due to friction which occurs can be avoided bycontactless transmission of the electrical power. An easy way of doingthat is represented by the asynchronous machine which is proposed inaccordance with the invention and whose rotor is connected to therotating part of the wind power installation, preferably to the rotatinghub, while the stator thereof is connected to the non-rotating part ofthe wind power installation, that is to say the machine carrier. Due toa relative movement therefore, as between the rotor and the rotatingstator field of the asynchronous machine, an electrical field is inducedin the rotor windings and in that way a voltage is produced in the rotorwindings. In that situation the asynchronous machine is operated in agenerator mode. The ac voltage induced in the rotor windings can then befurther processed with suitable further means for use for the desiredpurpose in the rotating part of the wind power installation.

The arrangement proposed in accordance with the invention for thecontactless transmission of electrical power suffers from losses to asubstantially lesser degree and is wear-free. The noise level generatedis drastically reduced, compared to the known use of slip rings.

Advantageous configurations of the invention are set forth in theappendant claims. The invention is preferably used in anelectromagnetically excited synchronous generator in order there toderive a direct current as an exciter current for the rotor of thesynchronous generator from the electrical power transmitted by theasynchronous machine. For that purpose there is preferably provided asuitable rectifier in the rotating part of the wind power installation,wherein in a further embodiment an LC filter can be connected on theinput side thereof in order to compensate for reactions of the polewheel of the synchronous machine, for example in the harmonics range.

In a further advantageous configuration of the invention there isprovided at least one further rectifier with which a dc voltage or alsoa direct current can be produced in order to supply further units on therotor unit of the wind power installation with electrical power. Forexample, provided for blade angle adjustment of the individual rotorunit blades are electric motors which are to be supplied with a dcvoltage. That supply is afforded in a simple manner in accordance withthe invention.

Preferably, arranged in the non-rotating part of the wind powerinstallation is an inverter with which an ac voltage is generated tofeed the stator of the asynchronous machine provided in accordance withthe invention, for power transmission purposes. That inverter preferablygenerates an ac voltage at a frequency of about 400 to 600 Hz.Advantageously, regulation of the exciter current of the rotor of thegenerator can even be effected in dependence on the speed of rotationand the electrical power of the generator, by means of the inverter. Inparticular the amplitude of the exciter current for the pole wheel of asynchronous generator can advantageously be regulated by the Inverter.

For many purposes within the rotor unit of the wind power installation,it is necessary for the dc voltage present to be as constant aspossible. For that purpose, besides a rectifier, it is also possible toprovide a capacitor which also additionally smoothes the output voltageof the rectifier. In order repeatedly to charge up that capacitor to thepeak value, it can therefore be provided that the inverter periodicallyproduces a voltage pulse. At the same time the capacitor serves as anintermediate storage device in order to provide sufficient electricalpower, even in the event of failure of the current supply, at least foran emergency adjustment procedure.

As the asynchronous machine is advantageously operated at a frequency of400 to 600 Hz and as there is an air gap from the primary winding to thesecondary winding, the asynchronous machine has a very high reactivecurrent requirement. That reactive current in accordance with theinvention can be provided if connected on the input side of the statorof the asynchronous machine is an LC filter for setting the reactivecurrent of the current fed to the stator.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention is described in greater detail hereinafter with referenceto the drawings in which:

FIG. 1 shows a circuit diagram of the solution according to theinvention, and

FIG. 2 shows the configuration of the voltage of an inverter for feedingthe asynchronous machine.

DETAILED DESCRIPTION OF THE INVENTION

The circuit diagram in FIG. 1 shows the solution according to theinvention for contactlessly transmitting electrical power from thenon-rotating part of the wind power installation to the rotating part.For that purpose there is firstly provided an inverter 1 which generatesan ac voltage at a frequency of 400 to 600 Hz, preferably about 500 Hz.Provided in the connecting lines between the inverter 1 and the stator 5of the asynchronous machine 4 are short-circuit limiting reactors 2 andLC filters 3 connected in a star circuit configuration. The ac voltageproduced by the inverter 1 and smoothed by means of the reactor chokes 2is thus fed into the non-rotating stator 5 of the asynchronous machine4. By virtue of the stator field which rotates in the stator windings,an electrical field is induced in the secondary windings of the rotor 6by virtue of the relative movement between the rotor and the statorfield and thus a voltage is produced in the stator windings.

The rotating stator 6 is mechanically connected to the hub of the windpower installation. The electrical power can thus be contactlesslytransmitted from the stationary part, that is to say the machine carrierof the wind power installation, to the rotating part, the rotor unithead.

The ac voltage induced in the rotor 6 is fed on the one hand to arectifier 8 which rectifies that ac voltage and the pole wheel 7 of theelectromagnetically excited synchronous generator of the wind powerinstallation. The rectifier 8 thus has an inductive load and the voltageacting at the pole wheel 7 is the effective root-mean-square value ofthe voltage. Preferably the inverter 1 regulates the output voltage insuch a way that the effective voltage at the output of the rectifier 1causes the desired direct current for the pole wheel 7 to flow. In thatsituation the high inductance of the pole wheel 7 smoothes the currentand evens out the waviness of the output voltage of the rectifier 8. Ifthe Inverter 1 produces high voltages for a short time, they arecompensated by the inductance of the pole wheel 7 if thereafter a lowervoltage is produced. It is therefore possible with the asynchronousmachine 4 In conjunction with the rectifier 8 to produce a regulateddirect current for the pole wheel 7. The amplitude of the excitercurrent for the pole wheel 7 should in that case be regulated independence on the rotary speed and the electrical power of thesynchronous generator by the inverter 1.

The ac voltage induced in the rotor 6 can also be used for furtherpurposes on the rotating part of the wind power installation. Thus forexample a rotor blade adjustment unit 10 requires a dc voltage. That dcvoltage is produced from the ac voltage of the rotor 6 by a rectifier11. That dc voltage is dependent on the amplitude of the output voltageof the rotor 6 as that involves peak value rectification.

The capacitors 12 are always charged up. In that respect the capacitanceof the capacitors 12 is such that the stored amount of current issufficient to actuate the rotor blade adjustment unit 10 of each rotorblade in the event of a power failure, in order to be able to securelyimplement emergency shut-down of the wind power installation androtation of the rotor blades 13 into the feathered position.

The transmitter 4 which is in the form of an asynchronous machinetherefore contactlessly delivers electrical power to the rotating partof the wind power installation, and that on the one hand supplies thepole wheel of the generator with a direct current and on the other handalso supplies further electrical units such as the rotor bladeadjustment unit with a dc voltage. For that purpose the inverter 1periodically produces a voltage pulse which repeatedly charges up thecapacitors 12 to the peak value. Such a voltage configuration in respectof the output voltage of the inverter 1 is shown in FIG. 2. It ispossible to clearly see the periodic voltage pulses P for charging upthe capacitors 12 to the required voltage. It has also been foundhowever that those peaks are not required but that the capacitors canalso be charged up without those peaks to a sufficiently high voltage toactuate the blade adjustment drive means.

The asynchronous machine 4 is preferably operated at a frequency ofabout 500 Hz and has an air gap from the primary winding to thesecondary winding. Those two conditions require a very high reactivecurrent requirement. The LC filter 3 is intended to produce that highreactive current. The pole wheel 7 which is connected on the output sideof the rectifier 8 also requires a very high reactive current. Itcomprises in part the fundamental oscillation and the harmonics such asfor example the fifth, seventh, eleventh and thirteenth harmonics. TheLC filter 9 comprising three star-connected branches each with a seriescircuit comprising a capacitor and a parallel circuit comprising aresistor and an inductor are intended to deliver that reactive power.Overall the level of efficiency of power transmission is enormouslyimproved by the two filters 3 and 9.

The solution according to the invention can thus easily provide forcontactlessly transmitting power from the non-rotating part of the windpower installation to the rotating part for different purposes. In thatrespect neither wear nor severe noise generation occurs.

All of the above U.S. patents, U.S. patent application publications,U.S. patent applications, foreign patents, foreign patent applicationsand non-patent publications referred to in this specification and/orlisted in the Application Data Sheet, are incorporated herein byreference, in their entirety.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1. A wind power installation for producing a sinusoidal ac voltagecomprising: a generator having a generator rotor and a generator stator;a rotor unit with rotor blades which is connected to the generatorrotor; and a power transmission means for the transmission of electricalpower from the non-rotating part of the wind power installation to therotor unit, the power transmission means having an asynchronous machinewhose stator is arranged at the non-rotating part of the wind powerinstallation and whose rotor is arranged at the rotor unit forcontactless transmission of electrical power to the rotor unit, andarranged in the non-rotating part of the wind power installation is aninverter for producing an ac voltage having a periodic voltage pulse forfeeding the stator of the asynchronous machine.
 2. A wind powerinstallation according to claim 1 characterised in that the generator isan electromagnetically excited synchronous generator and that providedat the rotor unit is a rectifier for conversion of the electrical powertransmitted to the rotor of the asynchronous machine into a directcurrent which is fed to the rotor of the generator as an excitercurrent.
 3. A wind power installation according to claim 2 characterisedin that a filter for adjusting the reactive current is connected on theinput side of the rectifier.
 4. A wind power installation according toclaim 1 characterised in that a rectifier is provided at the rotor forconverting the electrical power transmitted to the rotor of theasynchronous machine into a dc voltage, in particular for supplying arotor blade adjustment.
 5. A wind power installation according to claim1 characterised in that the inverter is adapted to regulate the excitercurrent of the rotor of the generator in dependence on the rotary speedand the electrical power of the generator.
 6. A wind power installationaccording to claim 1 characterised in that connected on the input sideof the stator of the asynchronous generator is an LC filter foradjusting the reactive current of the current fed to the stator.
 7. Awind power installation according to claim 1, further comprising: arotor blade adjustment unit that rotates the plurality of rotor bladesinto a feathered position during an emergency shutdown.
 8. A wind powerinstallation according to claim 7, further comprising: at least onecapacitor coupled to the rotor blade adjustment unit, such that anamount of stored current in the capacitor is sufficient to actuate therotor blade adjustment unit to rotate the plurality of rotor blades intothe feathered position during the emergency shutdown.